1. Field of the Invention
This invention relates generally to electrical accessory plugs, and more particularly to plugs of the type intended for installation in a cigar lighter socket or receptacle mounted in the dashboard or other panel of a motor vehicle or boat.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
U.S. Pat. No. 3,870,857 dated Mar. 11, 1975, issued to L. G. Horwitt and D. J. Mattis, and entitled CIGAR LIGHTER IGNITING UNIT, illustrates and describes a typical cigar lighter/socket assembly as commonly employed in automotive and/or marine vehicles. The socket is constituted as an electrically grounded well, with an electrically hot stud insulatedly mounted therein. The stud carries bimetallic fingers, by which electrical connection to the heating element cup of the ignitor plug is established when the igniting unit is inserted in the well.
Sockets of this general type can also accept accessory plugs similar to that shown in FIG. 15 of co-pending application U.S. Ser. No. 07/580,334 filed Sept. 10, 1990, in the names of Ali El-Haj, Donald J. Mattis, and Mark Michael, entitled POWER OUTLET FOR ELECTRICAL ACCESSORIES, and having common ownership with the present application.
Accessory plugs such as that illustrated generally have a cylindrical body which telescopes into the socket. The body in turn carries a contact or plunger at its inner end, for engagement with the head of the hot stud of the socket. The plug body usually has a side terminal in the form of a flat lug, which electrically contacts the inner surface of the socket, to complete the electrical circuit.
While plugs of this kind have met with wide acceptance in the field, and operate in a generally satisfactory manner, a number of drawbacks have become apparent. Due to the sliding fit between the plug body and the walls of the socket, the contact pressure at the pin is limited to that obtainable by the frictional engagement of the plug and socket walls. Where the pin surface is not perfectly clean, the electrical continuity can be marginal or erratic, causing undesirable heating at the points of contact, or arcing, which in turn leads to further contact degeneration.
In addition, due to the absence of any type of detent mechanism between the plug and socket, there exists an uncertainty as to what constitutes a fully inserted position of the plug. In use, the plug is merely inserted into the socket until mechanical resistance is encountered, and the user then assumes that the plug is fully seated, and positioned for use.